The only gear change from 2010 to 2011 was in the 2LS that was added mid 2011. It has the higher 2.92:1 gearing.
All v6 cars manual or automatic are having the issue but at slightly different rpms. So I don't think it is the transmission. To me it feels like a tuning issue, maybe even the VVT or simply reversion due to the firing order and exhaust manifold design combined with the VVT. Everyone needs to complain to your dealership for a fix. It is quite annoying, at least with the manual trans I can shift around it and keep my rpms out of that range. For me it happens worst at 2200 rpms (30 to 35 mph in third gear trying to hold a steady speed). Anyone who has had a Trifecta tune care to comment if the studdering went away? Anyone with long tube headers still have the problem?